I. Field
The following description relates generally to wireless communications systems, and more particularly to controlling access by mobile stations to femtocell access points of a wireless communications network.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so forth. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems including Evolved UTRA (E-UTRA), and orthogonal frequency division multiple access (OFDMA) systems. Each of the foregoing systems operates over licensed frequency spectrums, and licensee operators generally provide access to users according to a subscription model. The technology described herein pertains to these and similar systems.
An orthogonal frequency division multiplex (OFDM) communication system effectively partitions the overall system bandwidth into multiple (NF) subcarriers, which may also be referred to as frequency sub-channels, tones, or frequency bins. For an OFDM system, the data to be transmitted (i.e., the information bits) is first encoded with a particular coding scheme to generate coded bits, and the coded bits are further grouped into multi-bit symbols that are then mapped to modulation symbols. Each modulation symbol corresponds to a point in a signal constellation defined by a particular modulation scheme (e.g., M-ary Phase-Shift Keying (M-PSK) or Multi-Level Quadrature Amplitude Modulation (M-QAM)) used for data transmission. At each time interval that may be dependent on the bandwidth of each frequency subcarrier, a modulation symbol may be transmitted on each of the NF frequency subcarrier. Thus, OFDM may be used to combat inter-symbol interference (ISI) caused by frequency selective fading, which is characterized by different amounts of attenuation across the system bandwidth.
Generally, a wireless multiple-access communication system can concurrently support communication for multiple wireless terminals such as mobile stations that communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the mobile stations, and the reverse link (or uplink) refers to the communication link from the mobile stations to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels. Generally, each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized. A MIMO system also supports Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows estimation of the forward link channel from the reverse link channel. This enables an access point to transmit beam-forming gain on the forward link when multiple antennas are available at the access point.
In addition, a new class of small base stations for providing access to wireless communication systems has emerged, which may be installed in a user's home and provide indoor wireless coverage to mobile units using existing broadband Internet connections. Such a base station is generally known as a femtocell access point (FAP), but may also be referred to as Home Node B (HNB) unit, Home evolved Node B unit (HeNB), femto cell, femto Base Station (fBS), base station, or base station transceiver system. Typically, the femto access point is coupled to the Internet and the mobile operator's network via a Digital Subscriber Line (DSL), cable internet access, T1/T3, or the like, and offers typical base station functionality, such as Base Transceiver Station (BTS) technology, radio network controller, and gateway support node services. This allows a Mobile Station (MS), also referred to as a cellular/mobile device or handset, Access Terminal (AT) or User Equipment (UE), to communicate with the femtocell access point and utilize the wireless service.
Certain Wireless Access Points (WAP) for access to the Internet or similar wide area networks, for example, Wi-Fi access points under IEEE 802.11, sometimes control access by client devices using encryption schemes such as WEP, WPA or WPA2. Access to the WAP is provided to any device transmitting the key. However, key-based systems may have undesirable aspects for controlling access to a FAP for certain wireless communications systems. For example, a key-based system may not be desirable for some wireless communications systems operating on licensed bandwidth under a subscription model, because among other things access to the FAP can be controlled by any entity, for example a user, possessing the key. Therefore, new access control methods and apparatus are desirable for controlling access by mobile stations to femtocell access points.